1. Field of the Invention
The present invention relates to a method for preventing corrosion of Al and Al alloys. More particularly, the present invention relates to a method for preventing corrosion of Al and Al alloys to which halogen element-containing substances adhere. Furthermore, the present invention relates to a method for preventing corrosion of Al and Al alloys which have been pocessed by the dry-etching method.
2. Brief Description of the Prior Art
Al, Al-Si alloys and Al-Cu-Si alloys are used as materials of electrodes and wires of semiconductor devices and surface acoustic wave devices. These methods are recently practiced by the dry-etching technique for formation of patterns of electrodes or wires.
A halogen element-containing gas is used as a reactive gas as an atmosphere for dry-etching of Al or Al alloy. As a chlorine-containing gas used as the reactive gas, there are used HCl, BCl.sub.3, CCl.sub.4, PCl.sub.3, SiCl.sub.4, CCl.sub.3 F, C.sub.2 HCl.sub.3 and mixtures of two or more of these gases, and as a bromine-containing gas, there are used CHBr.sub.3, BBr.sub.3, PBr.sub.3, SiBr.sub.4 and mixtures of two or more of these gases. Furthermore, a mixture of a chlorine-containing gas and a bromine-containing gas and a mixture of a halogen-containing gas and other gas may be used.
A reactive gas such as mentioned above is introduced into an etching chamber, and micro-wave or high frequency field is applied to the reactive gas to cause glow discharge and by utilizing generated ions or radicals, Al or Al alloy having a mask of a photoresist or electron resist on the surface thereof is etched to effect fine processing.
When the processed sample is taken out into the open air after completion of the etching treatment, since the components of the reactive gas used for the etching operation adhere to the sample and they react with water contained in air, corrosion of Al or Al alloy is advanced. This phenomenon takes place in case of pure aluminum, but the phenomenon is conspicuous in case of Al alloy, especially Cu-containing Al alloy. Ordinarily, the Cu content in Cu-containing Al alloy used for semiconductor devices is 0.5 to 4% by weight. The higher is the Cu content, the more vigorous is corrosion by adhesion of the halogen components. Ordinarily, as the contents of impurities contained in Al alloy are increased, the degree of corrosion is increased.
From results of experiments made by us, it was confirmed that in case of Al alloys where the above-mentioned corrosion is vigorous, corrosion takes place within several minutes when the sample is taken out into the open air. Accordingly, even if a corrosion-preventing treatment is carried out after the lapse of this period, no substantial effect can be attained. Thus, it was confirmed that in order to prevent the above-mentioned corrosion in Al and Al alloys, it is necessary to carry out a corrosion-preventing treatment in a bell jar used for etching just after completion of the etching operation.
The above-mentioned corrosion of Al or Al alloy by adhesion of halogen components is caused not only in the process for manufacture of semiconductor devices but also in other fields.
The following references are cited to show the state of the art:
(i) U.S. Pat. No. 3,951,709, and PA1 (ii) U.S. Pat. No. 4,030,967.
Furthermore, Japanese Patent Application Laid-Open Specification No. 158343/79 (the patent application is now pending) can be cited as a prior application, though this is not a known prior art reference.